Plaque and calculi formed by calcification of plaque are causes of various oral diseases such as dental caries and periodontal diseases; therefore, a variety of plaque formation inhibitors and calculus formation inhibitors are proposed for the purpose of preventing such diseases. Plaque is a viscous mass attached to tooth surfaces and it is composed of oral flora and products thereof. The formation of plaque starts with the formation of a pellicle (acquired pellicle) made of saliva components on tooth surfaces. The pellicle is a build-up with amorphous patterns formed on tooth surfaces and saliva components such as sugar protein are adsorbed selectively onto the tooth surfaces. Plaque is formed as a result of adsorption and proliferation of bacteria in the oral cavity on the surface of the pellicle. Moreover, when rod-shaped bacteria such as those belonging to the genera Fusobacterium are adsorbed to other bacteria which have already been adsorbed to tooth surfaces, plaque formation is accelerated by the so-called coaggregation, that is, an adsorption reaction among bacteria in the oral cavity.
Bactericides and antimicrobial agents have conventionally been used widely as plaque formation inhibitors, and their effects, including an effect of reducing the number of bacteria in the oral cavity, are reported (Non-patent Document 1). It is however difficult to keep the effective concentration of them in the oral cavity because of a washing action of the saliva, so their effects are insufficient (Non-patent Document 2). Where plaque is already present, these agents weaken the metabolic activity of plaque bacteria, thus facilitating the deposition of minerals, i.e., calcification. As agents for inhibiting adsorption of bacteria to a pellicle, polysaccharides such as funoran and gellan gum are proposed (Patent Document 1). These agents, however, do not inhibit the formation of the pellicle per se; therefore, sometimes their effects are not satisfactory. As a calculus formation inhibitor, use of phosphorylated starch (Patent Document 2) and combined use of alginic acid and a divalent metal (Patent Document 3) are proposed. These inhibitors are used for symptomatic therapy and each of them can prevent only the crystallization of calcium phosphate and the like in plaque into calculi.
Polysaccharides such as xanthan gum, gum tragacanth, and sodium alginate are known to be useful as plaque formation inhibitors capable of inhibiting coaggregation of bacteria in the oral cavity (Patent Document 4).    [Patent Document 1] JP-A-05-139979    [Patent Document 2] JP-A-04-217613    [Patent Document 3] JP-A-08-175968    [Patent Document 4] JP-A-01-213222    [Non-patent Document 1] J. Periodental., 62(11), 649-651(1991)    [Non-patent Document 2] Oral Surg. Oral Med. Oral Pathol., April; 69(4), 444-449(1990)